The steel industry is an industry which consumes a large amount of energy, but about 40% of waste heat in a steel manufacturing process in accordance with a blast furnace method is non-used waste heat. In such waste heat, as a heat source which is easily recovered, but is not available in the related art, there is sensible heat of a high-temperature coke oven gas (crude COG) generated from a coke oven. Patent Document 1 and Patent Document 2 disclose a method for indirectly recovering sensible heat of crude COG. Specifically, Patent Document 1 or Patent Document 2 discloses that sensible heat is recovered by circulating a heat medium in a heat-transfer pipe provided inside an ascending pipe (or between the ascending pipe part and a dry main) of a coke oven. However, in this method, tar, light oil or the like accompanying crude COG is adhered to the outer surface of the heat-transfer pipe and is thus densified by carbonation and aggregation of the adhered material. As a result, deterioration in heat transfer efficiency over time or deterioration in heat exchange efficiency is inevitable. As a method for solving these problems, Patent Document 3 discloses coating of a catalyst such as crystalline aluminosilicate or crystalline silica on the outer surface of the heat-transfer pipe. According to this method, heat transfer efficiency can be stably maintained, since the adhered materials such as tar are decomposed into hydrocarbons with a low molecular weight through the coated catalyst. However, this method also enables indirect recovery of sensible heat of crude COG, but does not consider at all whether or not the decomposition product of heavy hydrocarbons such as tar becomes light hydrocarbons which are easily available as a gas fuel. In addition, this method does not consider deterioration of decomposition activity over time by a catalyst-poisoning sulfur compound such as hydrogen sulfide contained in a high concentration in crude COG.
There is almost no method which converts a reactive gas produced at a high temperature into chemical energy by incorporating a direct chemical reaction in the presence of a catalyst using the sensible heat. Almost all the cases in the related art are cases in which sensible heat in the form of a high-temperature gas is indirectly recovered (or not used at all) and the gas after cooling is treated and then used. Crude COG has sensible heat, but contains a sulfur compound in an amount higher than 2,000 ppm. Accordingly, it is thought to be substantially impossible to realize the method mentioned above from a viewpoint of designing the catalyst reaction by a decomposition reaction of heavy hydrocarbons such as tar. As described in Patent Document 4, NixMg1-xO—SiO2 spray drying solid solution catalyst, Ni/Al2O3 catalyst, active Al2O3 catalyst, Fe/Al2O3 catalyst and the like were reviewed, but the reforming activity of these catalysts was insufficient. In addition, an energy conversion catalyst is vulnerable to sulfur poisoning or carbon deposition. For this reason, it was difficult to prepare catalysts suitable for a decomposition reaction of tar composed of a condensed polycyclic aromatic material which may readily cause carbon deposition under an atmosphere containing a high concentration of sulfur compound, as mentioned above. In addition, when the reaction is performed and performance of the catalyst is then degraded, in a case where the catalyst is regenerated by air combustion, supported metal particles may be readily sintered (coarsened). For this reason, it is difficult to realize the reproduction of catalytic activity by regeneration.
In addition, besides the support method mentioned above, Patent Document 4 discloses a method for preparing catalysts for reforming hydrocarbons by mixing silica or alumina as a binder with a nickel magnesia compound, followed by spray drying, and a method for preparing catalysts for reforming hydrocarbons by physically adding a silica powder or an alumina powder to a nickel magnesia-based compound, followed by mixing. However, high catalytic activity or final product strength cannot be obtained with the method in which a silica powder or alumina powder is physically added to the nickel magnesia compound powder, followed by mixing, molding and baking.
Patent Document 5 discloses a method for obtaining purified COG used as fuels such as town gas or chemically synthetic materials by removing impurities (such as H2S, COS, aromatic hydrocarbon, tar and dust) contained in crude COG. In a case where a methanol synthetic plant is designed using COQ, there is a concern that the catalyst in the reforming apparatus thereof may be poisoned, since lower hydrocarbons or aromatic hydrocarbons remain in the purified COG obtained by the method. Accordingly, for example, Patent Document 6 discloses a preparation system in which pre-reforming is performed using a commercially available catalyst, and a synthetic gas is prepared using a reforming device. However, the document does not disclose a catalyst used for the reforming apparatus for preparing the synthetic gas in the latter part. That is, to date, there has been no research associated with the catalyst for reforming purified COG or crude COG containing a high concentration of tar.
Meanwhile, a great deal of research has been carried out for a long time on a catalyst for reforming methane, which is generally used as a material in reforming hydrocarbons.
For example, Non-Patent Document 1 suggests a catalyst prepared using a precipitate from a solution containing nickel, magnesium and aluminum, as a partial oxidation catalyst of methane.
Patent Document 7 discloses a catalyst in which oxide composed of nickel, magnesium and calcium is mixed with at least one of Group 3B elements, Group 4A elements, Group 6B elements, Group 7B elements, Group 1A elements and lanthanide elements.
Patent Document 8 discloses a catalyst which contains magnesium, aluminum and nickel as constituent elements and contains one or more elements selected from alkali metals, alkaline earth metals, Zn, Co, Ce, Cr, Fe and La.
Non-Patent Document 2 suggests a nickel-supported catalyst on ceria, zirconia, and ceria zirconia compounds, and magnesia- and nickel-supported catalyst on a ceria zirconia compound used for a tri-reforming reaction from methane to carbon dioxide, steam and oxygen.
Meanwhile, as catalysts which use sulfur-containing materials such as town gas, isooctane, kerosene and propane and generate hydrogen for fuel cells from relatively lower hydrocarbons, Patent Document 9 discloses a mixture of: a porous support composed of aluminum and magnesium; and oxides with at least one element selected from silicon, zirconium, cerium, titanium, aluminum, yttrium, scandium, Group 1A elements, and Group 2A elements.
In addition, as a catalyst which generates hydrogen from lower hydrocarbons such as propane, butane or town gas, there is a catalyst which contains magnesium, aluminum and nickel as constituent elements and further contains silicon, as mentioned in Patent Document 10.
However, hydrocarbons, which are the target of these catalysts, are readily decomposed to lower chain hydrocarbons. In addition, sulfur, which may poison catalysts, contained in the materials is limited to 50 ppm or less, as mentioned in Patent Document 9. That is, in relation to these known catalysts, no research was performed in regard to reforming of heavy hydrocarbons such as tar under a tar-containing gas atmosphere containing a high concentration of sulfur.
In addition, in accordance with the recent global warming problem, use of biomass, a carbonaceous material as an efficient method of reducing carbon dioxide discharge amounts has attracted much attention and research associated with performing high-efficiency energy conversion of biomass is being carried out. Recently, in addition, from the viewpoint of securing energy resources, research associated with the effective utilization of coal which has been actively pursued in the past has been reconsidered for practical application. Of these, regarding methods in which tar produced by carbonizing biomass is gasified to produce a crude gas (unpurified gas) and the sensible heat is used, technologies disclosed in Patent Document 11 or Patent Document 12 based on catalyst reforming of tar using a catalyst have been variously reviewed. However, the methods use expensive precious metals and thus have problems of low economic efficiency and short catalyst lifespan.